(1) Field of the Invention
This invention relates to novel imidazo[4,5-b]-pyridine compounds. The imadazo[4,5-b]pyridine compounds of this invention have excellent storage stability and can be used as drugs for the treatment of gastric and duodenal ulcers.
(2) Description of the Prior Art
In recent pathophysiological studies on gastric and duodenal ulcers, attention has been focused on the behavior of potassium ion-dependent adenosine triphosphase [hereinafter referred to as (H.sup.+ +K.sup.+) ATPase] participating in the production of hydrocholoric acid in the vesicles of the gastric endoplasmic reticulum, and the presence of an inhibitory effect on this enzyme is now considered to be a criterion of the usefulness of anti-ulcer agents (Gastroenterology, Vol. 1, p. 420, 1943; ibid., Vol. 73, p. 921, 1977). From this point of view, a class of compounds having a side chain comprising an unsubstituted to trisubstituted pyridylmethylsulfinyl group are now being developed as anti-ulcer agents, and one typical example thereof is Omeprazole having a benzimidazole skeleton (Japanese Patent Laid-Open No. 141783/'79; British Medical Journal, Vol. 287, p. 12, 1983). On the other hand, it has been confirmed or suggested that certain imidazopyridine compounds have an inhibitory effect on the aforesaid enzyme. Typical examples thereof are compounds of the general formula ##STR2## where one of X and Y is .dbd.CH-- and the other is .dbd.N--, R.sup.1' and R.sup.2' are each a hydrogen atom, a lower alkoxycarbonyl group, a halogen atom, a lower alkyl group, an amino group or a hydroxyl group and may be the same or different, R.sup.3', R.sup.4' and R.sup.5' are each a hydrogen atom, a lower alkoxy group or a lower alkyl group and may be the same or different, A is a lower alkylene group, and l is 0 or 1. However, when Y is .dbd.CH--, X is .dbd.N--, and l is 0, all of R.sup.3', R.sup.4' and R.sup.5' should not be hydrogen atoms. These compounds are reported in Japanese Patent Laid-Open No. 145182/'86 and will hereinafter be referred to tentatively as the well-known imidazopyridine compounds.
However, it has been found that, when stored without any preventive measure, Omeprazole undergoes a higher degree of deterioration than might be expected. In order to overcome its low storage stability, it has been imperative to convert Omeprazole into its alkali salt (Japanese Patent Laid-Open No. 167587/'84).
As to the well-known imidazopyridine compounds, the present inventors chose, as two typical examples thereof, 2-[2-(3,5-dimethyl-4-methoxy)pyridylmethylsulfinyl]-6-bromoimidazo[4,5-b]p yridine (hereinafter referred to tentatively as Compound .alpha.) and 2-[2-(3,5-dimethyl-4-methoxy)pyridylmethylsulfinyl]-6-methylimidazo[4,5-b] -pyridine (hereinafter referred to tentatively as Compound .beta.), and subjected them to various tests. As a result, it has been found that (1) similarly to Omeprazole, these compounds are also defective in storage stability and (2) while they exhibit a marked inhibitor effect on (H.sup.+ +K.sup.+) ATPase in the in vitro tests, this effect is not satisfactorily reflected in the in vivo tests for inhibitory effect on gastric secretion and for inhibitory effects on various experimental ulcers.